Life history variation across latitudes: observations between capelin (Mallotus villosus) from Newfoundland and the eastern Canadian Arctic

Life history trait variation within a species promotes regional-specific strategies that optimize fitness in a particular environment. Capelin (Mallotus villosus) is an important forage fish species with a circumpolar, temperate distribution, but has increased in relative abundance in Arctic regions recently. To examine for region-specific life history strategies, we compared life history characteristics (length, body condition, age of sexual maturity and growth) of spawning male capelin collected from the eastern Canadian Arctic, in Pangnirtung Fjord, Nunavut (66A degrees N; July 2014 and June-July 2015) with a sub-Arctic location on the northeast coast of Newfoundland (49A degrees N; July 2014 and 2015). First year growth was higher for sub-Arctic relative to Arctic capelin. In contrast, body condition (regression of total length versus mass) was lower for capelin in the Arctic compared to the sub-Arctic population. The age structure of spawning males suggested that Newfoundland capelin reached sexual maturity earlier, as the youngest spawners in Newfoundland were age 2+ (median age: 3+) relative to Pangnirtung where the median spawning age was 4+ (maximum age 5+). Overall, Arctic capelin were generally characterized by lower growth, especially in the first year, later age of reproduction, and lower body condition, relative to the sub-Arctic population. These differences may be the result of limited gene flow on the northern margins of this species' geographical distribution. They also support previously reported genetic distinction among the sub-Arctic and Arctic clades in the North Atlantic.